The present invention relates to machinery used to produce composite wood products, and in particular relates to improvements in rotating disk-type wood strand orienter machinery.
Composite wood products such as oriented strand board (xe2x80x9cOSBxe2x80x9d), particleboard and the like are produced from wood particles or strands. During the manufacturing process, strands of wood are typically formed into mats with the orientation of the wood strands controlled by strand-orienting machinery. Such strands are generally elongated (longer than they are wide), and when producing OSB it is desirable to have these strands aligned longitudinally and in a generally parallel fashion, and lying flat on the mat. Generally, the quality of a composite wood product depends in large part upon how well aligned the wood strands are in the wood strand mat produced by the orienter.
Commonly used strand orienters employ rotating disks. One type of orienter known in the art is the xe2x80x9cStokesxe2x80x9d type of orienter, which is described in detail in U.S. Pat. No. 3,115,431, which issued on Dec. 24, 1963 to Stokes et al. This orienter uses a plurality of intermeshed rotating disks mounted on a plurality of substantially parallel shafts oriented in a plane beneath a supply of wood strands. The wood strands are permitted to fall down upon the orienting disks, which, while turning, tend to align the strands longitudinally. The aligned strands fall between the disks to form a mat of strands on a platform or conveyor beneath the disks. The mat is accordingly formed of particles aligned generally longitudinally, although the strands are never perfectly aligned. The Stokes arrangement is shown in FIG. 1.
Another type of orienter known in the art, which also employs orienting disks, is the type known as the xe2x80x9cBxc3xcrknerxe2x80x9d orienter. The Bxc3xcrkner orienter is disclosed in U.S. Pat. No. 4,380,284, which issued on Apr. 19, 1983. In the Bxc3xcrkner orienter, disks on adjacent shafts are arranged in pairs in side-by-side relationship, defining passages for allowing strands of wood to pass through to form a mat. The Bxc3xcrkner arrangement is shown in FIG. 2.
The disclosures of the aforementioned Stokes and Bxc3xcrkner patents are incorporated herein by reference.
One continuing problem with wood strand orienters of the type discussed above is that many strands bridge two or more adjacent disks, riding along the tops of all of the disks and never falling through two adjacent disks onto the mat. These strands which bridge the orienting disks and which are carried along by successive disks over the orienter in its entirety are known in the art as xe2x80x9coversxe2x80x9d. It is typical to measure xe2x80x9coversxe2x80x9d as a percentage of starting material.
It is generally preferred to have adjacent disks in an orienter relatively close to one another, with narrow spacing (in the order of about 2 inches) between them. Closer disks tend to produce a mat having more highly-aligned strands. However, the closer the disks are to one another, the lower is the volume of material which is able to fall between adjacent disks. xe2x80x9cOversxe2x80x9d, therefore, are particularly problematic when the disks are relatively close together. The percentage of overs also tends to increase at higher material feed rates.
Various attempts have been made to try to ameliorate this problem. One example of a suggested solution will be found disclosed in U.S. Pat. No. 5,487,460, which issued on Jan. 30, 1986 to Barnes. In this patent, a xe2x80x9cmulti-deckxe2x80x9d orienter is described, which has three decks of orienting disk sets through which strands must fall, each successive deck purportedly aligning the strands to a greater degree. A similar arrangement may be found in U.S. Pat. No. 5,325,954, which issued on Jul. 5, 1994 to Crittenden et al. Crittenden shows a strand xe2x80x9cpre-orienterxe2x80x9d. In both the Crittenden et al and the Barnes patents, the spacing between the disks in the upper xe2x80x9cdeckxe2x80x9d is significantly larger than the spacing between the disks in the decks below them. However, it has been found Crittenden et al. and the Barnes arrangements occupy a large amount of space, and do not offer enough improvement in strand alignment over the Stokes and Bxc3xcrkner orienting arrangements to justify their implementation in commercial OSB manufacture.
A need remains, therefore, for a wood strand orienter particularly suited to orienting strands in substantially parallel relationship with a low amount of xe2x80x9coversxe2x80x9d at commercial material feed rates.
The present invention provides a system for improving wood strand orientation in a wood strand orienter having a plurality of axially-spaced, parallel orienter shafts positioned in a first plane, with each shaft bearing a plurality of axially spaced orienter disks. The system comprises a plurality of axially-spaced, parallel pre-orienting shafts positioned in a second plane above and substantially parallel to the first plane, the pre-orienting shafts substantially parallel to the orienter shafts; and a plurality of wheels mounted on each one of the pre-orienting shafts, each one of the wheels having a hub and a plurality of finger members extending radially outwardly from the hub. Each one of the wheels is positioned between two adjacent orienter disks and extends downwardly into a volume defined between the two adjacent orienter disks. Each one of the pre-orienter shafts may be positioned vertically above one of the orienter shafts.
The system of the present invention also provides means for rotating the pre-orienter shafts in a direction which causes the finger members to sweep against the direction of travel of wood strands along the tops of the orienter disks, thereby allowing the finger members to turn and straighten wood strands which are bridged over the tops of two or more of the adjacent orienter disks, allowing these strands to more readily fall between the disks. The wheels may have between 2 and 6 finger members.
In the preferred embodiment of the invention, one wheel is positioned between each pair of adjacent orienter disks, and is positioned more closely to one of the disks than to the other. The wheels may be spaced at 1.5 inch or 2 inch intervals, or at some other interval, depending upon the spacing of the orienter disks.